Canada : Global warming may reduce cod stocks to Arctic

Global warming and overfishing may yet defeat the Atlantic cod, a fish that so far has managed to survive even an ice age 21,000 years ago.

That's the message from an international group of scientists who published new research on cod stocks Wednesday in the journal Proceedings of the Royal Society B.

Grant Bigg, head of geography at the University of Sheffield in Britain and a co-author of the study, said the study marks the first time a link has been made between genetic analysis of the evolution of marine animals and modelling showing their habitat change over time.

Bigg said given climate change over the next century cod are likely to successfully spawn in the Arctic. "Whether the populations will be able to be large enough to be able to do that, being reduced in recent years from a combination of fishing and climate change already, is essentially unclear," he said in an phone interview Wednesday.

"This is a rapid change compared to their past ability to move between different areas."

The researchers say their paper demonstrates that the ability of the fish to survive extreme climate changes "suggests considerable inherent resilience" on the part of the cod.

But they warn future climate change and "human exploitation" could still negatively impact the fish.

Fishing pressures and low stocks have already increased concern over the current sustainability of cod and other fisheries, the researchers noted.

However, their research argues that even though natural climate change reduced the range of cod to approximately a fifth of what it is today, cod continued to populate both sides of the Atlantic.

That's no feat given that during the ice age 21,000 years ago habitat for the fish dramatically shrank as global sea level fell by 120 to 135 metres and large numbers of ice bergs scoured the sea floor and helped bring on abrupt climate change.

Bigg used a computer model to estimate ice age habits which were suitable for the fish. The analysis of the climate was combined with genetic studies by researchers at North Carolina's Duke University and the University of California and ecological data from scientists at the University of East Anglia and Norway's Institute of Marine Research.

Taken together, the research estimated where it was possible for the Atlantic cod to reproduce and survive. The scientists believe the ice age range of the fish extended as far south as Northern Spain, although the total area of habitat was restricted.

Nonetheless, the scientists concluded populations of cod continued to exist on both sides of the North Atlantic. They confirmed their findings using over a thousand DNA samples from present-day cod populations from Canada, Greenland, Iceland and around Europe.